Flow control system for load-handling apparatus



Feb. 27, 1962 J. E. OLSON ETAL FLOW CONTROL SYSTEM FOR LOAD-HANDLINGAPPARATUS Filed Oct. 20, 1958 2 Sheets-Sheet 1 TILT LOCK VALVE FIG.2

INVENTORS. JOHN E. OLSON yVlLLlAM P, DOWNEY BU CKHORN, CHEATHAM & BLOREATTORNEYS Feb. 27, 1962 .1. E. OLSON ETAL 3,022,773

FLOW CONTROL SYSTEM FOR LOAD-HANDLING APPARATUS Filed Oct. 20, 1958 2Sheets-Sheet 2 BYWILLIAM P. DOWNEY BUCKHORN,CHEATHAM 8 BLORE UnitedFiled st. 20, 1958. Ser. No. 768,224} 14 Claims. (Cl. 121-46) Thisinvention relates to a load-handling apparatus and particularly to suchapparatus having plural hydraulic means for causing movement of certainload-handling parts thereof, wherein the plural hydraulic means issupplied with hydraulic fluid from a common source. Illustrative of suchapparatus are industrial lift trucks having a pair of cylinders fortilting the truck mast, and straddle carriers of the type having fourcylinders for elevating the load shoes.

When a lift truck is turned, such as when rounding a corner, the load onthe forks tends to twist the mast. The two tilt cylinders, which controlthe position of the mast, permits such twisting when the cylinders areconnected to one another, because the fluid from one cylinder can crossover to the other cylinder. That is to say, fluid from the heavilyloaded cylinder can flow over to the lightly loaded cylinder. This isundesirable because the twisting which occurs places undue strain on themast and at times the mast tends to sway dangerously.

In a straddle carrier having hydraulic piston and cylinder means forelevating the load shoes, uneven positioning of the shoes is caused byan unsymmetrical load or by the uneven distribution of a load. That is,after the load has been lifted and the carrier is in condition fortravel, the more heavily loaded shoes will tend to descend and thelightly loaded shoes will tend to rise because the fluid from theheavily loaded cylinders will cross over to the lightly loadedcylinders. stresses in the parts.

A main object of the present invention is to provide a load-handlingapparatus of the type under consideration having means for preventingcross over of fluid between the cylinders after the load-handling partshave been moved to their desired positions, yet which means permits thecylinders to be connected together for the ready supply of fluid from acommon source.

A more specific object of the invention is to provide a load-handlingapparatus of the type just described equipped with a valve means havingcheck valves prohibiting cross over between the cylinders after thepositions of the pistons have been set, and yet permitting This createsundesirable either set of ends of the cylinders to be supplied withfluid under pressure, and the cylinders to be connected together for theready supply of fluid from a common source.

Another important object of the invention is to provide a load-handlingapparatus of the type under consideration wherein there are valve meansoperable to prevent cavitation in any of the cylinders, such as when thepistons are being moved in a direction with load assistance.

A further object of the invention is to provide a loadhandling apparatusof the type under discussion having flow divider means for causing theequal supply of fluid to the cylinders during movement of the pistons.

Various other objects of the invention will be apparent from thefollowing description taken in connection with the accompanying drawingswherein:

FIG. 1 is a side elevational view in diagrammatic form of a lift truckincorporating the hydraulic circuit of the present invention;

FIG. 2 is an outline of the truck as viewed from above showingschematically the hydraulic circuit;

3,@ZZ,773 Patented Feb. 2?, liifizi FIG. 3 is a diagrammatic view of astraddle carrier embodying the concepts of the present invention; and

FIG. 4 is a diagrammatic view of the hydraulic circuit connecting thevarious piston and cylinder units together.

Referring to the accompanying drawings and particularly to FIGS. 1 and2, the lift truck 9 has a mast 13 at its front end pivoted on the bodyof the truck for movement back and forth from a slightly rearwardlyinclined position to a forwardly inclined position shown in dottedlines. A fork carriage 14 is movable along the mast by conventionalmeans not necessary to describe. A pair of tilt cylinders 15 and 17 havepistons 25 and 27 connected by piston rods 35 and 37 to the mast 11.

Hydraulic fluid is supplied to and exhausted from the cylinders by theoperation of a pilot operated tilt lock valve 41 and a manually operateddirectional control valve 43, the latter being supplied with hydraulicfluid under pressure from a pump 45 through a line 47. The directionalcontrol valve is a three-position, four-connection valve having a closedcenter. However, when the directional control valve is in its closedposition there is a return line 48 from the pressure line 47 to a sump49. The directional control valve is actually a spool valve and thesymbols shown merely simplify the disclosure of the spool valve. Thesymbols correspond to the LLC. code.

When the spool member of the valve is shifted to the left astraight-trough portion 51 thereof is placed in alignment with the lines47 and 4S and with lines 53 and 55 so that fluid under pressure issupplied from line 47 to line 55 and fluid is delivered from the line 53to the sump 49. On the other hand, when the spool member of thedirectional control valve is shifted to the right, a reversing portion57 causes fluid under pressure to be delivered from the line 47 to line53, and enables fluid to be discharged from line 55 to the line 48 fordelivery to the sump 49. v The tilt lock valve 41 is actually a singlevalve in that all of the valve elements are contained within a singlebody. However, for convenience, the diagrammatic disclosure more clearlyshows the construction and operation of the valve. The line 55 isconnected to a pilot-operated spool valve 61, the valve being connectedby a line 63 to the cylinder 15 and by a line 65 to the cylinder 17. Inthe position of the spool member of the valve shown in FIG. 2, the innerends of the lines 55, 63 and 65 are closed to one another. The spoolmember of the valve 61 is normally biased by a spring 67 to the positionshown in FIG. 2. However, when the line 53 is supplied with fluidpressure, fluid under pressure will be supplied through a pilot line 68to the right-hand end of the valve 61 to cause a shifting of the spoolto the left to position a communicating portion 71 of the spool inalignment with the inner ends of the lines 63, 65 and 55 so that fluidfrom the lines 63 and 65 may exhaust through the line 55.

At the time that fluid under pressure is supplied to line 53, fluid willalso be supplied to the right-hand ends of the cylinders 17 and 15through branching lines 73 and 75. The line 55 is connected by a branchline 77 containing a check valve 79 to the line 65. The line 55 is alsoconnected by a branch line 81 containing a check valve 83 to the line63.

It may be assumed that when the pistons 25 and 27 move to the left, theyare moving with load assistance, that is, the weight of the load on theforns is urging the pistons to move toward the left, but when thepistons move to the right they are moving with load resistance. Theoperation of the circuit is as follows. It may be assumed that it isdesired to deposit a load and that the mast is in a vertical or slightlyrearwardly inclined position. To move the mast forwardly to facilitatedepositing the load readily, the pistons 25 and 27 need to be moved tothe left. However, they move to the left with 3 load assistance and thusthere is a tendency for cavitation to take place in the right-hand endsof the cylinders. However, cavitation is avoided, as will be nowexplained.

To-cause the pistons 25 and 27 to move to the left, the directionalcontrol valve spool member is shifted to the right to place thereversing portion 57 in the center of the'valve, therefore supplyingfluid under pressure to the pilot line 53 and to the right-hand ends ofthe cylinders 1'5 and 17 through the lines 73 and 75. When the spoolmember of valve 61 shifts to the left under the pressure of thehydraulic fluid supplied from line 53 and the pilot line 63, the innerends of the lines 63, -65 and 55 are connected together so that fluidfrom the right-hand ends of the cylinders 15 and 17 can flow into theline 55 and from there through the valve 43 and the line 48 to the sump.However, since the pistons 25 and 27 are already urged toward the leftby the load on theforks, there will be a tendency for the pressureWithin the right-hand ends of the cylinders 15 and 17 to drop and atendency for cavitation to take place. However, when the pressure doesdrop this means that the spool member of the pilot operated valve 61will move to the right under the influence of a spring 67 because thepressure in the line 53 is no longer sufficient to hold the valve memberin its left-hand position. By this arrangement, the pressure in theright-hand ends of the cylinders 15 and '17 is controlled so that itcannot drop below a predetermined value. Thus, the pistons 25 and 27 arein effect driven to the left even though they already have a tendency tomove to the left with load assistance.

Now it may be assumed that the load has been deposited or placed on thefolks and that it is desired to move the forks and the mast in thereverse direction. To do this, the spool member of the directional valve43 is shifted to the extreme right to place the straight-through portion51 in the center of the valve so that fluid under pressure is suppliedto the line 55, and the line 53 is connected to the sump 49. Since thereis no pressure in line 53, the spring 67 will move the spool member ofvalve 61 to the right to the FIG. 2 position so that the inner ends ofthe lines 63, 65 and 55 are not communieating with one another. However,the fluid under pressure in line 55 can reach the lines 63 and 65through the check valves 79 and 83, thus moving the pistons 25 and 27 tothe right and forcing fluid in the right-hand ends of the pistons outthrough the lines 73 and 75 and the line '53 to the sump 49. It will beappreciated that there is just suflicient pressure in the lines 73 and75 to cause such flow and this pressure is insufficient to operate thepilot operated valve 61.

After the mast has been moved rearwardly to the desired position, thespool member of the directional control valve is moved back to itscentral position, the position shown in FIG. 2, to hold the mast in thedesired position. It may now be assumed that the lift trick is beingmaneuvered around corners and the like and that the load tends to twistthe mast one way or the other. If the lines 63 and 65 were connected toone another, a twisting force on the mast tending to move the piston 25to the left and the piston 27 to the right would cause a cross over offluid from the left-hand end of the cylinder 15 to the left-hand end ofthe cylinder 17 thus enabling the mast to sway or twist. However, theinner ends of the lines 63 and 65 are not connected to one another andthe check valves 83 and 79 prevent communication of the lines 63 and 65through the medium of the branch lines 77 and 81. Thus, twisting orswaying of the mast is not possible.

FIG. 4 shows a basically similar circuit, with several differences to bepointed out, for controlling the supply and exhaust of fluid from thehydraulic piston and cylinder units of the straddle carrier 99, shown inFIG. 3. The straddle carrier is only diagrammatically disclosed and asshown includes four cylinders 101, 103, 105 and 107; the cylinders 101and 103 having pistons 111 and 4 113 connected by piston rods 121 and123 to a shoe 124, whereas the cylinders and 107 have pistons and 117having piston rods 125 and 127 connected to a shoe 129.

The circuit in FIG. 4 also includes a tilt lock valve 41a and adirectional control valve 43a, the latter being connected to a pump 45aby a line 47a, and to a sump 49a by a line 48a. There is a line'55a'connecting the directional control valve to a pilot-operatedvalve-61a.

The lower ends of the cylinders 101 and 103 are connected by lines 63aand 6311 through fluid motors 131 and 133 to the valve body of the pilotcontrol valve 61a. The lower ends of the cylinders 105 and 107 areconnected by lines 65a and 65b through fluid motors 135 and 137 to thevalve body of the pilot-operated valve 61a. A common shaft 13% connectsthe fluid motors 13-3 and 135 and a common shaft 141 connects the fluidmotors 131 and 135. A pair of gears 143 connects the shafts 141 and 139.Thus all the motors are driven in unison. This provides flowequalization and assures that equal quantities of fluid will be suppliedto the four cylinders.

A branch line 81a having a check valve 83a connects the line 55a to theline 63a, and a branch line 81b having a check valve 83b connects theline 55a to the line 63b. Also a branch line 77a having a check valve79a connects the line 55a to the line 65a, and a branch line 77b havinga check valve 79b connects the line 55a to the line 65!).

There is also a line 53a connecting the directional control valve 43a tothe upper ends of the cylinders 111 and 113 by means of a line 73a andto the upper ends of the cylinders 10S and 107 by a line 75a. There isalso a pilot control line 6811 from the line 53a to the pilot-operatedvalve 61a, the 'valve having a spring 67a opposing pilot operation. Thespool member of the valve has a communicating portion 71a shown in aninactive position in FIG. 4.

Another distinction between the basic arrangement disclosed in FIG. '4and that shown in FIG. 2 is that in FIG. 4 each of the pistons 111, 113,115 and 117 is equipped with a double-acting, pin-operated check valve151 in the case of piston 11 1, 153 in the case of piston 113, 155 inthe case of piston 115, and 157 in the case of piston 117. The type ofvalve per se is not new and thus is only diagrammatically disclosed.These check valves are opened when the pistons are driven upwardly tothe extreme ends of their strokes by the contact of the upper pins withthe associated ends of the cylinders to allow all four pistons to assumesimilar positions. This is required because even though the equal flowmeans in the form of the motors 131, 133, 135 and 137 are provided, overa considerable period of time, because of leakage and other factors,some inequality in the positions of the pistons 111, 113, 115 and 117 isencountered. Thus, when one piston reaches the end of its stroke priorto the others, flow of fluid through such pistons must be provided ifthe other pistons are to continue their movement, because the gearedpumps continue to supply fluid to all of the cylinders, including, ofcourse, the cylinder containing the one piston first mentioned. Thecheck valve of such one piston provides for such flow.

In operation, it may be assumed that it is desired to lift a load and todo this, the spool member of the valve 43a is moved upwardly, as theparts are shown in FIG. 4 to place straight-through portion 51a of thespool member in the center of the valve to supply fluid under pressureto the line 55a from whence fluid may be supplied through the lines 81aand 81b to the lower ends of the cylinders 101 and 103 and throughbranch lines 77a and 77b to the lower ends of the cylinders 105 and 107.The check valves 79a, 79b, 83a and 83b of course allow movement of thefluid under pressure to the lower ends of the cylinders because thecheck valves are upwardly opening as the parts are shown in FIG. 4. Thefluid in the upper ends of the cylinders is pushed through the exhaustlines 73a and 75a and the line 53a to the sump 49a. The fluid motorsassure that the pistons of the cylinders move upwardly in unison orsubstantially in unison.

When it is desired to lower a load, the weight of the load creates adownward force on the pistons and thus the the pistons of the cylindersmove downwardly with load assistance. This would tend to createcavitation in the upper ends of the cylinders, but again the circuitprovided prevents such cavitation because if the pressure in the lines73a and 75a drops below a predetermined value, this pressure is alsoeflective on line 53a and is insuflicient to maintain the spool member71a in an upward operative position. Thus, this regulates the pressurein the lines 530, 73a and 75a and prevents cavitation.

After a load is raised and the positions of the load shoes set, unequalloading of the shoes will not result in fluid cross over between thecylinders because at this time the valve 61a will be in its FIG. 4position. In such position, the lines 63a, 63b, 65a and 65b cannotcommunicate with one another through the valve 61a and cannotcommunicate with one another outside of the valve because of the checkvalves 83a, 83b, 79a and 79b. Thus the shoes will be maintained at thesame level despite uneven loading.

In the claims, the term plurality means two or more.

Having described the invention in what is considered to be the preferredembodiment thereof, it is desired that it be understood that theinvention is not to be limited other than by the provisions of thefollowing claims.

We claim:

1. In a load-handling apparatus, a load-handling means, a plurality ofcylinders, a plurality of pistons for said cylinders, each piston beingconnected to said loadhandling means, a source of fluid under pressure,a check valve for each cylinder, means for simultaneously connectingsaid source to one set of ends of said cylinders through said checkvalves in the direction of opening movement of said check valves, or forconnecting said source simultaneously to the other set of ends of saidcylinders, and means by-passing said check valves for exhausting fluidfrom said one set of ends.

2. In a load-handling apparatus, a load-handling means, a plurality ofcylinders, a plurality of pistons for said cylinders, each piston beingconnected to said loadhandling means, a source of fluid under pressure,a check valve for each cylinder, means for simultaneously connectingsaid source to one set of ends of said cylinders through said checkvalves in the direction of opening movement of said check valves, or forconnecting said source simultaneously to the other set of ends of saidcylinders, and means bypassing said check valves for exhausting fluidfrom said one set of ends, the last-named means including means forpreventing the exhaust of fluid from said one set of ends until pressurein the other set of ends of said cylinders has reached a predeterminedvalue.

3. In a load handling apparatus, a load-handling means, a plurality ofcylinders, a plurality of pistons for said cylinders, each piston beingconnected to said load handling means, a source of fluid under pressure,a check valve for each cylinder, means for simultaneously connectingsaid source to one set of ends of said cylinders through said checkvalves in the direction of opening movement of said check valves, or forconnecting said source simultaneously to the other set of ends of saidcylinders, and means by-passing said check valves for exhausting fluidfrom said one set of ends, the last-named means including means forpreventing the exhaust of fluid from said one set of ends until pressurein the other set of ends of said cylinders has reached a predeterminedvalue, said preventing means including a pilot-operated valve having avalve member movable under the influence of fluid pressure to a positionto connect said one set of ends with a discharge line, saidpilot-operated valve 6. being connected to the other set of ends ofsaidcylinders to be actuated-by the pressure therein.

4. In a flow control system for a load-handling apparatus having aplurality of piston and cylinder units, the pistons of which are to beforced away from one set of ends of the cylinders with load assistanceor forced away from the opposite set of ends of said cylinders with loadresistance, means for connecting either set of ends of said cylinderswith a source of fluid under pressure and for exhausting fluid fromeither set of ends of said cylinders in correlatedin-one-end-out-the-other-end manner, said means including valve meansresponsive to the pressure in said one set of ends for preventing theexhaust of fluid from said other set of ends until a predeterminedpressure has been built up in said one set of ends to prevent cavitationin said one set of ends.

5. In a flow control system for a load-handling apparatus having aplurailty of piston and cylinder units, the pistons of which are to beforced away from one set of ends of the cylinders with load assistanceor forced away from the opposite set of ends of said cylinders with loadresistance, means of connecting either set of ends of said cylinderswith a source of fluid under pressure and for exhausting fluid fromeither set of ends of said cylinders in correlatedin-one-end-out-the-other-end manner, said means including means forpreventing the exhaust of fluid from said other set of ends until apredetermined pressure has been built up in said one set of ends toprevent cavitation in said one set of ends, said preventing meansincluding a pilot-operated valve having a valve member movable under theinfluence of fluid pressure to a position to connect said other set ofends of said cylinders with a discharge line, said pilot-operated valvebeing connected to said one set of ends of said cylinders'to be actuatedby the pressure therein.

6. In a load-handling apparatus of the type set forth in claim 1 inwhich said check valve and the last-named means prevent cross-over offluid between said one set of ends in the static condition of saidpistons.

7. In a load-handling apparatus of the type set forth in claim 2 inwhich said check valve and the last-named means prevent cross-over offluid between said one set of ends in the static condition of saidpistons.

8. In a load-handling apparatus of the type set forth in claim 1 inwhich there are flow regulating means for said cylinders providing forequal flow to and from said one set of ends of said cylinders to providefor equal movement of said pistons despite diiferences in loadingthereof.

9. A load-handling apparatus of the type set forth in claim 4 in whichthere are flow regulating means for said cylinders providing for equalflow to and from said other set of ends of said cylinders to provide forequal movement of said pistons despite diflerences in loading thereof.

10. In a straddle carrier, a plurality of vertically mounted cylindershaving pistons with depending piston rods, load engaging means connectedto said rods, a source of fluid under pressure on said carrier, a checkvalve for each cylinder, reversing valve means for simultaneous- 1yconnecting said source to the lower set of ends of said cylindersthrough said check valves in the direction of opening movement thereof,or for connecting said source simultaneously to the upper set of ends ofsaid cylinders, and means by-passing said check valves for exhaustingfluid from said lower set of ends.

11. In a straddle carrier of the type set forth in claim 10, in whichthe last-named means constitutes valve means responsive to the pressurein said upper set of ends of said cylinders for preventing the exhaustof fluid from said lower set of ends until a predetermined pressure hasbeen built up in said upper set of ends to prevent cavitation in saidupper set of ends.

12. In a straddle carrier of the type set forth in claim 11, in whichthere are flow regulating means for said cylinders providing for equalflow to and from said lower set of ends of said cylinders to provide forequal movement of said pistons despite difierences in loading thereof.

13. In a straddle carrier having a wheel supported body providing atunnel-like load space between the wheels of the body for accommodatingthe load to be handled, a pair of load engaging members at the side ofthe load space, a pair of vertical double-acting cylinders for each shoeof each load engaging member, means mounting the upper ends of thecylinders on said body, each cylinder having a piston and a rodextending therefrom and projecting from the lower end of said cylinder,means connecting the rods to sm'd shoes, a source of fiuid underpressure on said body, a reservoir on said body for said source, a checkvalve for each cylinder, each check valve being connected to the lowerend of its cylinder so as to open toward the cylinder in response to thesupply of fluid under pressure from said source, but close in responseto pressure from said cylinder, valve means connected to said reservoirand connected between said source and all said check valves, said valvemeans having independent connections to the upper end of said cylindersand having a first position in which fluid from said source is conductedto said check valves and fluid from the upper ends of said cylinders isexhausted to said reservoir, and a second position in which said sourceis connected to the upper ends of said cylinders, and other valve meansconnected between the lower ends of said cylinders and said reservoirindependently of said check valve and responsive to a predeterminedpositive pressure in the upper ends of said cylinders for moving to openpositions to place said lower ends in communication with said reservoir.

14. In a straddle carrier having a wheel supported body providing atunnel-like load space between the wheels of the body for accommodatingthe load to be handled, a pair of load engaging members at the side ofthe load space, a pair of vertical double-acting cylinders for each shoeof each load engaging member, means mounting the upper ends of thecylinders on said bod each cylinder having a piston and a rod extendingtherefrom and projecting from the lower end of said cylinder, meansconnecting the rods to said shoes, a source of fluid under pressure onsaid body, a reservoir on said body for said source, a check valve foreach cylinder, each check valve being connected to the lower end of itscylinder so as to open toward the cylinder in response to the supply offluid under pressure from said source, but close in response to pressurefrom said cylinder, valve means connected to said reservoir andconnected between said source and all said check valves, said valvemeans having independent connections to the upper end of said cylindersand having a first position in which fluid from said source is conductedto said check valves and fluid from the upper ends of said cylinders isexhausted to said reservoir, and a second position in which said sourceis connected to the upper ends of said cylinders, and other meansconnected between the lower ends of said cylinders and the firstmentioned valve means independently of said check valves and responsiveto a predetermined positive pressure in the upper ends of said cylindersto move to an open position to place said lower ends of said cylindersin communication with the first mentioned valve means, said first namedvalve means in its second position placing said other valve means incommunication wtih said reservoir.

References Cited in the file of this patent UNITED STATES PATENTS2,420,554 Mott May 13, 1947 2,467,576 Zimmermann Apr. 19, 1949 FOREIGNPATENTS 740,429 Great Britain Nov. 9, 1955

